1. Field of the Invention
The present invention relates to processes for preparing 3,4-dicyano-1,2,5-thiadiazole. In particular the present invention relates to processes for preparing 3,4-dicyano-1,2,5-thiadiazole which has the formula: ##STR1## starting from diaminomaleonitrile (DAMN), which is a tetramer of hydrocyanic acid, a known commercially available intermediate for organic syntheses.
2. The Prior Art
3,4-DICYANO-1,2,5-THIADIAZOLE (I) is a known compound having known uses as intermediate for organic syntheses in general (polyamides, pigments, adhesives), besides being itself useful as a fungicide and bactericide.
Moreover, 3,4-dicyano-1,2,5-thiadiazole (I) can be used to obtain 1,2,5-thiadiazol-3,4-dicarboxylic acid, which is a starting material (monomeric compound) for the preparation of polyamide polymers used in forming efficient membranes for reverse osmosis. The technology based on the use of said membranes for reverse osmosis is of particular interest, for example, in desalting waters.
The known methods of preparing 3,4-dicyano-1,2,5-thiadiazole are based on (1) destructive oxidation of 4-nitro-2,1,3-benzothiazole with KMnO.sub.4, the former being obtained from 3-nitrophenylenediamine and S.sub.2 Cl.sub.2, or (2) by reaction of hydrocyanic acid, chlorine and SCl.sub.2 or sulphur in a solvent (chlorinated) in the presence of trimethylamine.
These methods are of little use for commercial scale operations because of the low yields and complicated separation and purification operations required.
In fact, the destructive oxidation methods involve particularly large amounts of impurities, while the preparation starting from HCN, chlorine and SCl.sub.2 or sulphur is complicated by the presence of solvents and catalysts (for example trimethylamine) which must be removed and recovered.
It is an object of this invention to provide processes for preparing 3,4-dicyano-1,2,5-thiadiazole in a simple and economical way, without the disadvantages of the known methods.
Another object is to provide processes for preparing 1,2,5-thiadiazole-3,4-dicarboxylic acid that are practicable on a commercial scale.